If I signed up for iTunes match. After everything is up in the cloud. Could I then delete all my music in my iTunes app to save space? Also if I cancelled it would my music be there if I were to sign back up again?

To what I know once the music is on the icloud you can access it on any of your device. You can store up to 25,000 songs in iCloud the good thing about it is that only the files you want to play would be stored on your phone or device which enables you to have a huge playlist on your device without taking up too much space. As long as you back up your music on i cloud you can delete the ones on your playlist and just restore them from i cloud.